Anachronistic Adaptation: An Empirical Test of the Response-Readiness Theory

Abstract

Common, heritable mental illnesses constitute a considerable challenge for evolutionary models of human behavior. Attention-Deficit/Hyperactivity Disorder (ADHD), a neurodevelopmental disorder characterized by hyperactivity, impulsivity and inattention, is especially difficult to reconcile with evolutionary theory given its high prevalence and association with considerable dysfunction. Response-readiness theory attempts to explain ADHD as an evolutionary mismatch, which occurs when previously adaptive traits are rendered maladaptive by environmental change. Particularly, response-readiness theory frames ADHD as an adaptation to environments that are dangerous, resource scarce, unpredictable, and harsh (i.e., the environmental adversity hypothesis), arguing that inattention facilitated environmental scanning, important in detecting threats in unpredictable environments (i.e., the hypervigilance hypothesis), whereas hyperactivity facilitated investigative exploration, vital in orienting to novel and unfamiliar environments (i.e., the exploratory hyperactivity hypothesis).Study One tested the environmental adversity hypothesis, indicating that harsh and unpredictable childhood environments were associated with inattention, whereas unpredictability alone was associated with hyperactivity. Study Two tested the hypervigilance hypothesis, conceptualizing hypervigilant threat detection in terms of both the proficient detection of threats, as well as a more general bias to perceive threats in ambiguous cues. Although the latter conceptualization was supported, the former was not. Study Three tested the exploratory hyperactivity hypothesis, indicating that inattention, not hyperactivity, was indirectly associated with exploratory information seeking in both domain-general and domain-specific contexts, and that these relationships were mediated by individual differences in intolerance of uncertainty. Although providing only mixed support for response-readiness theory, the results of this project present an opportunity to break new theoretical ground, particularly in the development of the hyperactive facilitation theory. This theory advocates for the contextualization of response-readiness within a larger differential susceptibility framework. Informed by the present results, the proposed theory frames hyperactivity as a mechanism of development plasticity (i.e., the readiness spectrum hypothesis), intolerance of uncertainty as a vital motivator of investigative exploration, orienting ancestral individuals to unfamiliar environments (i.e., the uncertainty reduction hypothesis) and inattention as a cognitive filter, necessary for coping with the informational demands of environmental unpredictability (i.e., the attentional filter hypothesis), The implications of each novel hypothesis are discussed, followed by recommendations in testing them.